Involute Roll Angle (creo parametric 10)

Forum|Forum|10 months ago
June 4, 2025
3 replies
809 views

Hello Everyone,

I am having a hard time trying to calculate the roll angle for a involute curve. I can draw it as shown in the image but unable to calculate it. I've been working with the involute roll angle formula but i have not been able to make match what you see below in the picture.

Any help world be great,

And thank you in advance.

Sean

General

tbraxton

22-Sapphire II

Your question, if there is one is not clear. Are you asking how to use Creo Parametric functions to calculate the roll angle? You have not disclosed the equation that you have to determine the roll angle in your post.

If you have the equation, then you can use relations in the Creo model to calculate the roll angle assuming all of the values/variables of the function are defined in the model.

https://support.ptc.com/help/creo/creo_pma/r11.0/usascii/index.html#page/fundamentals/fundamentals/About_Relations_1.html

You can use relations to control the modeling process in the following ways:

•To control the effects of modifications on models

•To define values for dimensions in parts and assemblies

•To set constraints for design conditions. For example, by specifying the location of a hole in relation to the edge of a part.

•To describe conditional relationships between different parts of a model or assembly

S

sblack

Author

4-Participant

Tbraxton,

I apologize for the incomplete statements.

My question is when I calculate the involute roll angle I am getting a different angle than what is shown in the picture.

1. Involute curve created by datum curve equation that is put in the picture.

2. Roll angle formula I'm using: Inv(a) = Tan(a)-a,

a = pressure angle in Radians

Picture Roll angle is 1.096322 degrees but my calculated roll angle is 1.094738 degrees.

tbraxton

22-Sapphire II

If you are able to, post your model and note what version of Creo you are working in.

Rounding errors may account for this difference or the inputs to the calculation are not identical to those used in the Creo geometry. It is hard to say without access to the model features and any calculations (inside or external to Creo) you have been making. Do you have access to a gear calculator that is a known good design tool for calculating these values?

What method are you using to calculate the roll angle value of 1.094738 degrees? For your purposes would you consider the analytical solution (equation) for the roll angle to be the design target? Would you expect the sketched (graphical solution) to match the analytical angle value to some number of significant figures?

Your picture posted implies that you consider the angle value from the Creo sketch to be the target value, if this is so why would you use this value rather than the value calculated from the equation? Is your pressure angle of 21.661111 degrees a design input or calculated within Creo?

C

Chris3